A field-emission cathode (or field emitter) emits electrons upon being subjected to an electric field of sufficient strength. The electric field is produced by applying a suitable voltage between the cathode and an electrode, typically referred to as the anode or gate electrode, situated a short distance away from the cathode.
When a field-emission cathode is utilized in a flat-panel CRT display, electron emission from the cathode occurs across a sizable area. The electron-emitting area is commonly divided into a two-dimensional array of electron-emitting portions, each situated across from a corresponding light-emitting portion to form part or all of a picture element (or pixel). The electrons emitted by each electron-emitting portion strike the corresponding light-emitting portion and cause it to emit visible light.
It is generally desirable that the illumination be uniform (constant) across the area of each light-emitting portion. One method for achieving uniform illumination is to arrange for electrons to be emitted uniformly across the area of the corresponding electron-emitting portion. This typically involves fabricating the electron-emitting portion as a group of small, closely spaced electron-emissive elements.
Various techniques have been investigated for manufacturing electron-emitting devices that contain small, closely spaced electron-emissive elements. Spindt et al, "Research in Micron-Sized Field-Emission Tubes," IEEE Conf. Rec. 1966 Eighth Conf. Tube Techniques, 20 Sep., 1966, pp. 143-147, describes how small randomly distributed spherical particles are employed to define the locations for conical electron-emissive elements in a flat field-emission cathode. The size of the spherical particles strongly controls the base diameter of the conical electron-emissive elements.
In fabricating an electron-emitting diode having a thick anode, Spindt et al first creates a structure in which an upper molybdenum layer overlies an intermediate dielectric layer situated on a lower molybdenum layer. Spherical polystyrene particles are scattered across the upper molybdenum layer after which "resist", typically alumina, is deposited on top of the structure. Openings are created through the resist by removing the spheres, thereby lifting off portions of the resist situated on the spheres.
The upper molybdenum is etched through the resist openings to create openings through the upper molybdenum. The intermediate dielectric layer is etched through the openings in the resist and upper molybdenum to form cavities through the dielectric layer down to the lower molybdenum. The resist is removed, typically during the cavity formation.
Finally, molybdenum is evaporatively deposited on top of the structure and into the cavities in the intermediate dielectric layer. The evaporation is performed in such a way that the openings through which the molybdenum accumulates in the dielectric cavities progressively close. Conical molybdenum electron-emissive elements are formed in the dielectric cavities, while a continuous molybdenum layer that combines with the upper molybdenum layer to form the anode for the diode simultaneously accumulates on the upper molybdenum.
The utilization of spherical particles to establish the locations, and base dimensions, of electron-emissive elements in Spindt et al is a creative approach to creating an electron-emitting device. However, the electrons emitted by the electron-emissive cones are collected by the directly overlying anode and thus are not utilized to directly activate light-emitting areas. It would be desirable to utilize spherical particles to define the locations for small, closely spaced electron-emissive elements that emit electrons which can be employed to directly activate light-emissive elements in a flat-panel device in a highly uniform manner.